This invention relates to a device for treating air, and particularly for removing contaminants such as particulates like dust or pollen, germs, viruses or gaseous components from the air for domestic purposes.
Previous devices of this type have been large and bulky, frequently greater than 30 to 40 cm across.
This is because in order to treat a reasonable throughput of air in a room or office the product of fan speed and fan area has to be fairly large, and if a small fan is used it therefore has to run at a high speed. At higher speeds however fans tend to produce an unacceptable level of noise which makes them unsuitable for domestic or office applications.
Moreover, filters for such applications having a mesh size sufficient to trap particles no greater than 0.1 xcexcm provide a considerable resistance to the flow of air; hence to provide a sufficient throughput of air to clean the air in a room satisfactorily such air purifiers have traditionally been large, to stand on a desk or even the floor.
A need therefore exists to provide an air treatment device adapted to be plugged directly into and be supported by an electrical socket, in particular, a mains electrical socket.
According to the invention there is provided an air treatment device adapted to be plugged directly into and supported by a mains electrical socket, the device comprising a treatment medium, a fan adapted to cause air to flow through the treatment medium, an electric motor to drive the fan, a housing, and a plurality of pins attached to the housing and adapted to fit within the socket and to provide electricity to the motor, wherein the fan includes an integral hub adapted to accommodate the motor in the hub to facilitate support of the device by the electrical socket. Most simply the pins themselves, which supply electricity and therefore power to the motor, also provide the support for the device itself.
Alternatively, or in conjunction with the above, the invention provides an air treatment device adapted to be plugged directly into and supported by an electrical socket comprising a treatment medium, a fan adapted to cause air to flow through the treatment medium, a motor to drive the fan, a housing and a plurality of pins attached to the housing adapted to fit within the socket and to supply electricity to the motor wherein the axial thickness of the fan is between 1 and 5 centimeters, preferably between 2 and 4 centimeters.
Alternatively, or in conjunction with the above, the invention provides an air treatment device adapted to be plugged directly into and supported by an electrical socket comprising a treatment medium, a fan adapted to cause air to flow through the treatment medium, a motor to drive the fan, a housing and a plurality of pins attached to the housing adapted to fit within the socket and to supply electricity to the motor wherein the motor is adapted, in use, to rotate the fan at less than 3000 revolutions per minute, preferably between 2000 and 2800 revolutions per minute.
Alternatively, or in conjunction with the above, there is provided an air treatment device adapted to be plugged directly into and supported by an electrical socket comprising a treatment medium, a fan adapted to cause air to flow through the treatment medium, a motor to drive the fan, a housing and at least two, preferably three, pins attached to the housing adapted to fit within the socket and to supply electricity to the motor wherein the device is so dimensioned to be supported solely by the fitting of the pins within the electrical socket.
In all of the above, the motor is most conveniently a DC motor, which means that for installation on a normal mains socket transforming and rectifying means also have to be included. Surprisingly, the inventors have found that even with this constraint it is still possible by careful design to construct a treatment device that can support itself in a socket. The transformer and associated rectifier elements can be located above the fan. Local regulations determine the maximum size of articles adapted to be supported from a mains socket and in particular a maximum torque allowed to be exerted on the socket.
The treatment medium is preferably a filter, in particular an electrostatic filter, comprising a fine-mesh sheet. The fabric for such filters is suitably made of polypropylene which is electrostatically charged during manufacture and is available, for example, from 3M . The filter operates by electrostatically attracting small particles passing through it. The filter sheet is advantageously puckered or ribbed, not flat, to increase the effective surface area of the filter for a given size of housing. The ribbing also acts to slow the effective speed of air through the filter, so that the electrostatic filter can still trap particles even with a relatively high volumetric throughput of air. Such a throughput is necessary to provide effective cleaning of air.
Alternatively, for gaseous pollutants the choice of treatment medium will depend on the exact chemical nature of the gas but may include activated charcoal and molecular sieves.
As outlined above and in use, the speed of the fan is preferably less than 3000 rpm, further preferably between 2000 and 2800 rpm. Above 3000 rpm the noise and pitch of the sound of the fan becomes too irritating for use in a domestic or office environment. Below approximately 2000 rpm it is not possible to provide a fan having sufficient throughput and creating a suitable pressure differential. Electrostatic filters require tightly controlled pressure differentials and volumetric throughputs to operate correctly.
In order to achieve a suitable throughput the fan is preferably of the reverse-curve impeller type with at least six, preferably between nine and fifteen blades. The reverse-curve impeller is able to produce a sufficient throughput because it is able to produce a sufficiently high pressure drop across the filter, unlike a conventional fan of the same size. If the number of blades is too small the fan has to be rotated too quickly to provide an adequate throughput of air. Too high a number of blades increases the manufacturing difficulties and reduces the size of the gaps between the blades to an extent that the efficiency is not increased by adding further blades.
The dimensions of the fan are also preferably carefully selected. If the blades of the fan are too close to the housing the amount of noise is greatly increased. However, if the fan is too small then it has to be run at a faster speed for the same throughput of air, which once again increases the noise. Experiments have shown that the outside end of the fan blades should be between 1 mm and 20 mm from the inside of the housing, further preferably between 3 and 8 mm. Typically, the fan will have a diameter of from 1 to 14 cm, preferably 2 to 8 cm.
It will be appreciated that if the fan has an excessive axial thickness (depth) then the housing becomes excessively large and too much torque has to be borne by the mains electrical socket. Accordingly the axial thickness or depth of the fan is also important, although less critical that the diameter in terms of throughput of the fan. Thus, as outlined above, the depth of the fan should be between 1 and 5 cm.
The housing of the device is preferably between 5 and 15 cm across a face of the device opposed to the face of the device adjacent the mains socket in use. The distance between the opposed faces, i.e. the depth of the device, is between 1 and 15 cm, preferably between 2 and 11 cm, most preferably between 3 and 8 cm. A larger device could not be supported by a mains electrical socket and in dual-socket arrangements would interfere with the neighbouring socket, and a smaller device would not clean the air effectively.
The motor can be of conventional construction but is preferably designed to run continuously for an extended period.
In addition to filtering air by drawing it through the treatment medium, for example, the filter, the device may be adapted to treat air by emitting components into the air. These components may include fragrances, odour neutralising agents, aromatherapy oils, insect repellents or insecticides. Such components may be included on or in the treatment medium or they be emitted into the air in another manner from or by the device.